The project is devoted to elucidating mechanisms responsible for the hypercoagulable state and developing methodology for studying mucopolysaccharide-antithrombin interactions under a variety of conditions; specifically we intend: (a) to examine the interaction of hemostatic system enzymes with antithrombin and highly active heparin. (b) to determine the structural basis of heparin's anticoagulant action. (c) to probe the molecular details of heparin-antithrombin-enzyme interaction. (d) to analyze heparin fractions with multiple binding sites for antithrombin. (e) to study the pharmacologic function of highly active heparin and the physiologic function of heparin-like molecules on the vessel wall.